Failure rate targets for automotive technologies are fairly stringent e.g. typically below 1 ppm. On the other hand, the reliability margin for CMOS (complementary metal oxide semiconductor) devices is reduced and the electrical fields increased with decreasing feature size. For thin gate oxides and especially for high-k dielectrics a new methodology is needed to allow such high electric fields. Due to this decreased reliability margin, the first dielectric breakdown is no longer regarded as a hard fail for a digital circuit. Instead, a progressive phase is allowed where the integrity of the dielectric is permitted to steadily decrease until a hard failure occurs. The electric fields for isolation dielectrics such as inter-metal dielectrics, shallow trench isolation, deep trench isolation, etc. are also increased. This is especially true if higher voltages are used in CMOS technologies for power applications with DMOS (double-diffused metal-oxide-semiconductor), BEOL (back-end-of-the line) capacitors such as VPP (vertical parallel plate) capacitors, grid capacitors, sandwich capacitors, etc. and similar devices.
As with thin dielectrics where transistor and resistor limited breakdown and even digital circuits such as ring oscillators and logic elements are used to assess the product relevant breakdown or degradation behaviour such as NBTI (negative bias temperature instability) and HCS (hot carrier stress), conventional stress by an external circuit delivers too much energy and usually results in a hard breakdown of the dielectric. An external resistor can help mitigate this problem, but the external circuitry and equipment used to stress the dielectrics still dominate the degradation behaviour and therefore render the assessment of the breakdown/degradation behaviour unreliable. In addition, the cables used to connect the external circuitry and test equipment to the semiconductor wafer under stress charge during stressing and discharge when dielectric breakdown occurs, further increasing the external influences on the dielectric breakdown/degradation behaviour.